Repair of digital television set-top box

The fleet of analogue TVs is rather reluctant to give way to digital equipment, gradually taking “second” places - in the kitchen, in offices, garage workshops, etc. At the same time, DVB-T2 set-top boxes are also carried. We have already managed to evaluate the advantages of the latter; some owners also appreciated the disadvantages - the rather low reliability of these devices. As a rule, one of the weakest points of this kind of equipment is the switching power supply - most cases of failure are associated precisely with a malfunction of the power supply, and a malfunction of the power supply can entail such serious consequences that repairing the device will be impossible. And yet, using the example of two digital TV set-top boxes, the possibility of repairing them independently will be considered here. The first device was TVK 3101. When turned on, the image had severe distortion and periodically disappeared completely. A few days later, the set-top box began to turn off a few seconds after the manufacturer's logo appeared on the screen.



The second device is the Oriel 740 set-top box. This device did not respond to commands from the remote control, the indicator barely glowed red.



After opening the console cases, it turned out that in both cases the electrolytic capacitors of the secondary power filters were swollen.



It should be borne in mind that when working with the set-top box, special care should be taken - the primary power supply rectifier converts an alternating voltage of 220 volts into a constant voltage of about 300 volts, and this potential remains at the terminals of high-voltage electrolytic capacitors for some time after the power is removed - up to several tens of seconds . In the pictures they are located between the pulse transformers and the plugs of the power cords. Before working with the device board, these capacitors must be short-circuited through a resistor with a resistance of 51-62 kOhm.



Both faulty capacitors turned out to be almost the same - 1000 µF, 10 V. The picture shows one of them. The fact that its lid looks barely deformed should not give you the slightest confidence in the serviceability of the part - even if some part of the container has been preserved, such a part will have an increased leakage current, which is unacceptable. When replacing, you should select capacitors with the same operating voltage or with a slightly higher one, as in the picture - instead of a 10-volt part, a 16-volt part is shown, and with the same dimensions. Of course, faulty parts should be replaced with new ones, not used ones - otherwise the repair will soon have to be repeated.



After replacement, we turn on the set-top box - the indicator lights up brightly, the device responds to remote control commands, the image is stable. But the renovation is not finished yet...



There are traces of flux on the board - solder paste, rosin... Through such a coating, high-frequency currents can quite easily pass wherever they want. As a result, over time we may get an unstable image, noise, etc. troubles.Therefore, carefully wash the board with a cotton swab moistened with alcohol or acetone. After such cleaning, wipe the board with a dry cotton swab.




We install the board in place, check - it works.



Now we assemble the console completely and check its functionality again.



We check the second device in the same way - the device is working normally, the repair is completed.



In conclusion, I will add that the quality of the antenna amplifier power supply also greatly affects the operation of the set-top box. Thus, if the capacity of the filter capacitor is insufficient, signal loss is possible - there have been cases of complete loss of channels of the second multiplex. To recognize a malfunction of the antenna power supply, it is enough to replace it with a DC source of 9-12 volts (for example, a Krona battery or a battery from a computer uninterruptible power supply). If the reception quality improves, you should replace the antenna power supply with a known good one.